The invention relates to a process for the treatment of tobacco and similar organic materials,
in which the material is impregnated with an inert organic liquid and is heated above the boiling point of this liquid by the introduction of a hot gas, whereby the liquid is vaporized with simultaneous expansion of the material, and PA1 in which recovery of a portion of the vaporized liquid is effected after the expansion while a residual amount remains in the material.
A process of this type is known on the basis of DE-A-19 17 552 and DE-A-22 03 105. In the known processes, tobacco is impregnated with liquid or vaporous inert organic compounds. The impregnation agent is vaporized during a subsequent heat treatment with a gas such as steam whereby the tobacco expands, i.e., a delamination and volume enlargement of the tobacco takes place. In order to reduce to a minimum the extraction of the soluble components which are normally present in the tobacco that is to be treated, the impregnating fluid should be introduced into the tobacco in a vaporous state. This permits a reduction in the amount of the impregnation agent required. During the tobacco expansion, its filling capacity is increased by 60 to 120%. The impregnation agent which vaporizes during the expansion is removed together with the gas. The expansion agent can be recovered from the mixture. A disadvantage of the known process is that a residual amount of the impregnation agent remains in the expanded tobacco. In order to remove these residual amounts from the expanded tobacco, it is necessary to store the tobacco over longer periods of time until the impregnation agent has evaporated. Such storage times, however, constitute lost time in the treatment of the tobacco and they require corresponding storage facilities equipped for the conditioning of tobacco. The residual amounts removed by the storage can only be recovered with great difficulty.
According to U.S. Pat. No. 3 828 797 it is known to carry out the expansion of tobacco by subjecting tobacco impregnated with a volatile, organic liquid to a microwave treatment. In that process the total energy required for vaporizing the expansion agent is introduced in the form of microwaves. Such an energy-rich treatment with microwaves, however, involves extraordinary difficulties on a large production scale because an overheating of the tobacco material can easily occur during the complete vaporization of the expansion agent. It is practically impossible to regulate the microwave energy in such a way that complete vaporization of the expansion agent is achieved without overheating of the tobacco. Furthermore, the energy consumption of this known process is very high. Even though the process functions well under laboratory conditions it is difficult to execute on a large production scale.
A process is described in an older (not previously published) application, EP 86 105 606.7, in which the residual amount of impregnation agent that remains in the tobacco after the expansion is removed from the tobacco by subjecting the tobacco to a microwave treatment, whereby the residual amount of the impregnating liquid is vaporized and is withdrawn for recovery. This process entails a considerable space requirement and the amount of the material treated per unit time can be varied only to a limited extent for a given size of installation, any increases in the amount treated being obtainable only with great difficulty. Moreover, an expensive control system is necessary. In a few exceptional cases such as the case of a control system that is not properly synchronized or is defective, it is possible that the tobacco would lump together and lead to non-uniform microwave treatment. The possibility would then exist that the impregnation agent might not be removed completely from the deeper layers of the tobacco.